1. Technical Field of the Invention
The present invention relates to a manufacturing method for U-bolts. More particularly, it relates to a manufacturing method for U-bolts made of fiber reinforced plastics (hereinafter referred to as simply "FRP") in which fiber is oriented in three dimensional directions wherein the manufacturing method for U-bolts is superior in terms of mass-productivity.
2. Prior Art
Generally, when attaching and fixing metal pipes employed as piping to wall surfaces or the like, it is often the case that U-bolts of the same material as used for the metal pipes are employed in terms of corrosion-resistivity. In recent years, piping made of resin are promoted for utilization as piping due to reasons such as being light-weighted or being superior in view of corrosion-resistivity. For example, piping used in septic tank peripheries which are embedded underground for which corrosion-resistivity is required and which are cost-consuming in terms of maintenance have been gradually changed to piping made of resin.
However, there are still being used conventional metallic U-bolts as U-bolts for fixing these piping made of resin and thus provide problems in terms of maintenance etc., since these U-bolts suffer, for instance, from corrosion.
Accordingly, there have been increasingly used U-bolts made of FRP which are light-weighted, corrosion-resistant, and which further present sufficient strength and conclusive force.
When manufacturing U-bolts made of FRP, it is required to make the direction of orientation of fiber included in the FRP to be three-dimensional (e.g. to be meshed) so that the fiber does not get finely cut by thread portions which might cause a decrease in strength of thread or damages thereof.
When manufacturing U-bolts made of FRP, the following steps had been conventionally taken: a linear or tape-like member made of FRP with fiber being oriented in three-dimensional directions is cut to a specified length, bent into U-shape and hardened by heating etc. Thereafter, threads are formed at tip portions of the hardened U-shaped portions.
Since each article was individually produced in manufacturing methods for U-bolts made of FRP, the efficiency was quite poor and inadequate for mass-production. Further, since such a method results in large irregulars in quality of manufactured U-bolts, it is also difficult to improve the reliability of the product.
The present invention has been made to solve such problems, and it is an object of the present invention to provide a manufacturing method for U-bolts wherein U-bolts are made of FRP in which fiber is oriented in three-dimensional directions and which is superior in terms of mass-productivity.